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Multiple vendor SFTP logging format string vulnerability

Vulnerability Note VU#419241

Original Release Date: 2006-02-13 | Last Revised: 2006-02-15

Overview

A logging function used by multiple vendors' SFTP servers contains a format string vulnerability, which may allow an authorized remote attacker to execute arbitrary code or cause a denial of service.

Description

SFTP

SFTP (Secure FTP) is a file transfer application that uses SSH for encryption.

The problem

The logging function of several vendors' SFTP servers contains a format string vulnerability.

Vulnerable products include:

    • Reflection for Secure IT UNIX Server version 6.0
    • Reflection for Secure IT Windows Server version 6.0
    • F-Secure SSH Server for Windows version 5.x
    • F-Secure SSH Server for UNIX version 3.x through 5.x

Impact

A remote authenticated attacker may be able to execute arbitrary code with the privilege of the user or cause a denial of service to the SSH server.

Solution

Upgrade or patch


AttachmateWRQ Reflection for Secure IT and F-Secure SSH Server users should install an upgrade, as specified in WRQ Tech Note 1882.


According to the WRQ Tech note, the following workaround may prevent exploitation of the vulnerability:

On UNIX Servers

   1. Edit the SSH server's sshd2_config file:

         1. Change the line

            subsystem-sftp internal://sftp-server

            to

            subsystem-sftp sftp-server

            Note: This change disallows the use of chroot.

         2. Comment out the SftpSyslogFacility keyword line. Note: The line should begin with two "pound" signs, as in this example:

            ## SftpSyslogFacility LOCAL7

   2. Restart the SSH server to read the changes in the configuration file.

On Windows Servers
The only workaround is to disable the sftp subsystem as follows:

   1. Edit the SSH server's sshd2_config file and comment out the subsystem-sftp line. Note: The line should begin with two "pound" signs, as in this example:

            ## subsystem-sftp "fsshsftpd.exe"

   2. Restart the SSH server to read the change in the configuration file.

Vendor Information

419241
 
Affected   Unknown   Unaffected

F-Secure Corporation

Notified:  January 16, 2006 Updated:  February 15, 2006

Status

  Vulnerable

Vendor Statement

Products Affected:

Reflection for Secure IT UNIX Server version 6.0
Reflection for Secure IT Windows Server version 6.0
F-Secure SSH Server for Windows version 5.x
F-Secure SSH Server for UNIX version 3.x through 5.x


Problem Correction:

AttachmateWRQ Reflection for Secure IT and F-Secure SSH Server users should install an upgrade, as specified in WRQ Tech Note 1882 ( http://support.wrq.com/techdocs/1882.html).

The following workaround may prevent exploitation of the vulnerability: On UNIX Servers
1. Edit the SSH server's sshd2_config file:
1. Change the line
subsystem-sftp internal://sftp-server
to
subsystem-sftp sftp-server
Note: This change disallows the use of chroot.
2. Comment out the SftpSyslogFacility keyword line. Note: The line should begin with two "pound" signs, as in this example:
## SftpSyslogFacility LOCAL7
2. Restart the SSH server to read the changes in the configuration file.

On Windows Servers
The only workaround is to disable the sftp subsystem as follows:
1. Edit the SSH server's sshd2_config file and comment out the subsystem-sftp line. Note: The line should begin with two "pound" signs, as in this example:
## subsystem-sftp "fsshsftpd.exe"
2. Restart the SSH server to read the change in the configuration file.

AttachmateWRQ also recommends that you bookmark and regularly check the Security Updates and Reflection for Secure IT web page for the latest information about updates and vulnerabilities:
http://support.wrq.com/techdocs/1910.html

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

WRQ, Inc.

Updated:  February 15, 2006

Status

  Vulnerable

Vendor Statement

Products Affected:

Reflection for Secure IT UNIX Server version 6.0
Reflection for Secure IT Windows Server version 6.0
F-Secure SSH Server for Windows version 5.x
F-Secure SSH Server for UNIX version 3.x through 5.x


Problem Correction:

AttachmateWRQ Reflection for Secure IT and F-Secure SSH Server users should install an upgrade, as specified in WRQ Tech Note 1882 ( http://support.wrq.com/techdocs/1882.html).

The following workaround may prevent exploitation of the vulnerability: On UNIX Servers
1. Edit the SSH server's sshd2_config file:
1. Change the line
subsystem-sftp internal://sftp-server
to
subsystem-sftp sftp-server
Note: This change disallows the use of chroot.
2. Comment out the SftpSyslogFacility keyword line. Note: The line should begin with two "pound" signs, as in this example:
## SftpSyslogFacility LOCAL7
2. Restart the SSH server to read the changes in the configuration file.

On Windows Servers
The only workaround is to disable the sftp subsystem as follows:
1. Edit the SSH server's sshd2_config file and comment out the subsystem-sftp line. Note: The line should begin with two "pound" signs, as in this example:
## subsystem-sftp "fsshsftpd.exe"
2. Restart the SSH server to read the change in the configuration file.

AttachmateWRQ also recommends that you bookmark and regularly check the Security Updates and Reflection for Secure IT web page for the latest information about updates and vulnerabilities:
http://support.wrq.com/techdocs/1910.html

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Bitvise

Notified:  January 16, 2006 Updated:  January 17, 2006

Status

  Not Vulnerable

Vendor Statement

Our SSH server for Windows, WinSSHD, does not share codebase with affected versions of AttachmateWRQ's server. Thus, WinSSHD is not affected by this vulnerability.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

InterSoft International

Notified:  January 16, 2006 Updated:  January 18, 2006

Status

  Not Vulnerable

Vendor Statement

The referenced VU #419241 does not apply to any of the products

produced by InterSoft International, Inc.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

MacSSH

Notified:  January 16, 2006 Updated:  January 16, 2006

Status

  Not Vulnerable

Vendor Statement

No statement is currently available from the vendor regarding this vulnerability.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

The MacSSH author indicates:

Neither MacSSH nor MacSFTP are exposed to this vulnerability.

If you have feedback, comments, or additional information about this vulnerability, please send us email.

OSSH

Notified:  January 16, 2006 Updated:  January 16, 2006

Status

  Not Vulnerable

Vendor Statement

No statement is currently available from the vendor regarding this vulnerability.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

The OSSH author indicates:

I'm quite sure that the now very
old ossh does not include a sftp client or server and that it should
thus not be vulnerable.

Either way ossh is old and obsolete and I don't recommend its use.

If you have feedback, comments, or additional information about this vulnerability, please send us email.

PuTTY

Notified:  January 16, 2006 Updated:  January 16, 2006

Status

  Not Vulnerable

Vendor Statement

PuTTY's SSH and SFTP implementations are not derivatives of anybody
else's. In addition, the PuTTY code base does not include an SSH or
SFTP server at all. We cannot be affected by this issue.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

VanDyke Software

Notified:  January 16, 2006 Updated:  January 17, 2006

Status

  Not Vulnerable

Vendor Statement

VanDyke Software's VShell(R) Server for Windows and VShell

Server for UNIX products are not affected by the issues
described in VU#419241. VShell does not share any common
SFTP code with Reflection/F-Secure products.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

FiSSH

Notified:  January 16, 2006 Updated:  January 16, 2006

Status

  Unknown

Vendor Statement

No statement is currently available from the vendor regarding this vulnerability.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

OpenSSH

Notified:  January 16, 2006 Updated:  January 16, 2006

Status

  Unknown

Vendor Statement

No statement is currently available from the vendor regarding this vulnerability.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Pragma Systems

Notified:  January 16, 2006 Updated:  January 16, 2006

Status

  Unknown

Vendor Statement

No statement is currently available from the vendor regarding this vulnerability.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

TTSSH

Notified:  January 16, 2006 Updated:  January 16, 2006

Status

  Unknown

Vendor Statement

No statement is currently available from the vendor regarding this vulnerability.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

WinSCP

Notified:  January 16, 2006 Updated:  January 16, 2006

Status

  Unknown

Vendor Statement

No statement is currently available from the vendor regarding this vulnerability.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

lsh

Notified:  January 16, 2006 Updated:  January 16, 2006

Status

  Unknown

Vendor Statement

No statement is currently available from the vendor regarding this vulnerability.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

View all 14 vendors View less vendors


CVSS Metrics

Group Score Vector
Base N/A N/A
Temporal N/A N/A
Environmental N/A

References

Acknowledgements

Thanks to WRQ for reporting this vulnerability.

This document was written by Will Dormann.

Other Information

CVE IDs: None
Severity Metric: 3.38
Date Public: 2006-02-13
Date First Published: 2006-02-13
Date Last Updated: 2006-02-15 14:51 UTC
Document Revision: 9

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